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72 TRG-TRC007-EN
Glossary
hertz (Hz) The unit of measure for frequency. One hertz is equal to one cycle
per second.
insertion loss (IL) The difference in sound pressure measured in a single
location, with and without a noise control device (installed between the source
and receiver) in place.
near field The area adjacent to the source where sound does not behave as
it would in a free field, due to the fact that the source does not radiate sound
equally in all directions.
NEBB National Environmental Balancing Bureau (www.nebb.org)
noise Unwanted or obtrusive sound. Generally, people object to sound when
it interferes with speech, concentration, or sleep.
noise criteria (NC) A single number used to describe sound in a room. It uses
a series of curves for plotting sound pressure by octave band and determining
the NC value.
noise reduction (NR) A term used to measure the effect of a barrier on
reducing the amount of transmitted sound. It is the difference between sound-
pressure measurements taken on each side of a barrier.
noise reduction coefficient (NRC) A single number used to describe the
sound-absorbing characteristics of a material. It is the arithmetic average of
the absorption coefficients for the 250, 500, 1,000 and 2,000 Hz octave bands.
octave band A range of frequencies that is defined such that the highest
frequency in the band is two times the lowest frequency. The octave band is
identified by its center frequency.
phon A unit of measure, using a logarithmic scale, used to describe the
loudness of a sound.
pitch A subjective quantity used to describe a sound. It is primarily based on
frequency, but is also dependent on sound-pressure level and composition.
Pitch is not measured, but is described with terms like bass, tenor, and soprano.
receiver sound correction The relationship between the sound energy (sound
power) entering the room and the sound pressure at a given point in the room
where the receiver hears the sound. This reduction is due to a combination of
effects, including distance and the absorptive and reflective properties of the
surrounding surfaces. Also called room effect.
reflected sound The sound that bounces off, or is reflected by, a barrier back
toward the source.
regenerated sound The noise caused by turbulent flow in air and water
systems.